Proximity switch assembly

ABSTRACT

A proximity switch assembly for signalling the location of a movable member at either of opposite end limits of movement relative to a stationary frame includes a compact elongate housing adapted to be mounted on the frame to extend along the path of movement of a power driven member, such as a piston rod, which shifts the movable member between its end limits. A proximity switch is fixedly mounted in the housing and a switch actuating member is mounted for sliding movement over a relatively short distance sufficient to move an actuating tab into and out of actuating proximity to the switch. Lost motion abutment means on the switch actuating member and the power driven member move into engagement with each other as the power driven member approaches each end of its stroke to move the actuating member within actuating proximity to the switch as the movable member arrives at one end limit and to move the actuating member out of actuating proximity to the switch as the movable member arrives at its opposite end limit.

BACKGROUND OF THE INVENTION

The present invention is directed to a proximity switch assemblyparticularly adapted for use in signaling the location of a movablemember at either of two end limits of movement. Although not so limitedin application, the switch assembly of the present invention isespecially adapted for use in power actuated clamps of the general typeshown in my prior patent 4,396,183 in which a clamping arm is driven inmovement between a closed workpiece clamping position and an openposition by the piston rod of a fluid pressure actuated motor.

Such clamps are widely employed in automotive aassembly plants to clampmajor sheet metal panels, such as roof panels, body side panels, andfloor panels in a fixed position while the panels are being welded toeach other. In the so called "framing station" disclosed in U.S. Pat.No. 4,162,387 a basic vehicle body assembly constituted by a floorpanel, opposite side panels and a roof panel loosely assembled to eachother is advanced into the framing station between a pair of clampcarrying "gates" which are then advanced to fixedly clamp the opposedside panels to locate the floor, side and roof panels in their finalassembled position. While so clamped, robotic welding devices weld thepanels to each other.

Systems such as that disclosed in U.S. Pat. No. 4,162,387 employnumerous power actuated clamps of the type referred to above, and inthis completely automated system it is essential that all clamps beclosed prior to the welding operation, and that this fact be verified bythe control system before the robotic welders begin their welding cycle.Similarly, the control system must verify that all clamps are openbefore the retraction of the gates to accommodate the discharge of thewelded body from the framing station.

While the detection of a clamp in its open or closed position could beaccomplished by a conventional limit switch, the service life andreliability of exposed mechanically actuated limit switches in a roboticwelding environment is unsatisfactory.

It has been proposed, see U.S. Pat. No. 4,316,145, to employ acommercially available magnetically biased reed switch, generallyreferred to as a proximity switch, mounted in the clamp actuatinghydraulic cylinder to detect the arrival of the piston at either end ofits stroke. The latter arrangement presents the advantage that theswitch itself, due to its mounting in the cylinder, is shielded fromdirt, weld splatter, etc., and the switch does not require any directmechanical contact with a moving part in order to generate the desiredsignal. However, the arrangement disclosed in patent 4,316,145 requiresthe employment of two proximity switches, one to sense the arrival ofthe piston at each end of its stroke, the cylinder end cap must bemodified to provide a mounting for the switch and normally a junctionhousing must be mounted on the exterior of the cylinder for eachproximity switch. As noted above, in robotic welding systems, numerousclamp assemblies must be employed and mounted upon the gate at locationsdetermined by the configuration of the body panel, rather thanconvenience, and substantial operating clearances must be provided formovement of several robotic welding heads which must pass through thegate to reach the seams which they are to weld.

The present invention is directed to a proximity switch assembly usefulin the environment described above which is of extremely compactconstruction, requires a minimum of structural modification of aconventional power actuated clamp, and which requires only a singleproximity switch whose contacts are located in one position when theclamp is clamped and remain in that one position until the clamp iscompletely open, at which time the contacts are shifted to their otherposition until the clamp is again at its clamped position.

SUMMARY OF THE INVENTION

In a typical power actuated clamp, the clamp assembly includes a housingadapted to be mounted on a fixed frame and a hydraulic motor fixedlymounted upon the housing with its piston rod disposed to be reciprocatedwithin the housing. A clamping arm pivotally mounted on the housing andcoupled to the piston rod by a link in a manner such that straight linemovement of the piston rod drives the clamping arm in pivotal movementbetween the clamp open and clamped closed position.

In accordance with the present invention, a proximity switch fordetecting the arrival of the clamp at its closed or its open position ismounted in a relatively close fitting housing which is in turn mountedon the clamp housing to extend along and cover an elongate slot throughthe clamp housing wall which extends in adjacent parallel relationshipto the path of movement of the piston rod of the clamp actuating motor.An elongate proximity switch actuator is slidably mounted within theswitch housing for limited sliding movement parallel to the piston path.The switch actuator includes a projecting actuator tab mounted on theactuator in adjacent spaced relationship to the proximity sensingelement of the switch to be moved into and out of actuating range of thesensing element by the sliding movement of the actuator relative to thefixed housing.

A pair of facing abutment shoulders are mounted on the actuator membernear its opposite ends and are spaced from each other by a distanceslightly less than the stroke of the piston rod between the clamp closedand clamp open position. A pin or abutment is mounted on the piston rodor some element movable with the piston rod to project through the slotin the clamp housing into the space between the opposed abutmentshoulders on the proximity switch actuator member. As the piston rodmoves to one end limit of movement, representing for example the clampopen position, the pin or abutment carried with the piston rod willengage one of the shoulders on the proximity switch actuator and slidethis actuator relative to the switch to move its tab into actuatingrange of the sensing element of the switch to close the switch contacts.

Upon subsequent movement of the piston rod toward the clamp openposition, the pin or abutment will be disengaged from the aforementionedshoulder, leaving the switch in its "on" condition, and as the pistonrod arrives at its clamp open position, the piston rod carried abutmentwill engage the opposite abutment shoulder on the actuating member toslide that member in a direction moving the actuating tab out ofactuating proximity with the switch to open the switch contacts. Thecharacteristics of the switch are such that this shifting movement ofthe actuating tab need only be about 1/10th of an inch between itsswitch "on" and switch "off" positions, hence shifting of the switchfrom one condition to the other is essentially simultaneous with thearrival of the clamp at its clamp closed or its clamp open position.

Other objects and features of the invention will become apparent byreference to the following specification and to the drawings.

IN THE DRAWINGS

FIG. 1 is a side elevational view showing a proximity switch assemblyembodying the present invention mounted upon a typical power actuatedclamp, with certain parts broken away or shown in section;

FIG. 2 is a partial side elevational view of the clamp of FIG. 1 withthe proximity switch assembly and one side plate of the clamp housingremoved;

FIG. 3 is a detailed cross-sectional view taken on line 3--3 of FIG. 1;and

FIG. 4 is a detailed cross-sectional view taken on line 4--4 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, a power actuated clamp designated generally10 is fixedly mounted upon a frame 12 which in turn fixedly mounts astationary workpiece engaging jaw 14 conformed to the shape of aworkpiece W. The clamp assembly 10 includes a housing 16 upon which ismounted the cylinder of a hydraulic motor 18 whose piston rod 20projects into the housing. A clamping arm 22 is mounted in housing 16for pivotal movement about a pivot 24. Arm 22 carries a jaw 26 conformedto fixedly clamp workpiece W against stationary jaw 14 when the clampingarm is positioned as shown in FIG. 1 by piston rod 20.

Referring now to FIG. 2, in which the housing side plate closest to theobserver in FIG. 1 has been removed, it is seen that piston rod 20 iscoupled to clamp arm 22 by a link 28 connected at one end by pivot 30 toclamp arm 22 and connected at its opposite end to piston rod 20 by apivot 32. Referring now particularly to FIG. 2, it is seen that pivot 32projects outwardly beyond the opposite sides of piston rod 20 and thatthe projecting ends of pivot 32 are received within elongate slots 34,36 formed in the opposed housing side walls. This arrangement guides andsupports the distal end of piston rod 20 in straight line movementthroughout its entire stroke.

Referring now to FIG. 1, a proximity switch assembly designatedgenerally 38 is fixedly mounted at the outer side of that side wall ofhousing 16 through which the slot 36 passes to completely overlie slot36.

Switch assembly 38 includes a housing 40 having a removable cover 42which provides access to an elongate chamber 44 within the housing. Thebottom of chamber 44 is defined by a wall 46 from which a pair ofmounting flanges 48 project to engage the walls of slot 36 in the sidewall of clamp housing 16. A square nut 50 slidably received and retainedin grooves 53 in the side walls and bottom of chamber 44 threadablyreceives a proximity switch 52 to support switch 52 within chamber 44and do accommodate longitudinal adjustment of switch 52 relative tohousing 40.

Proximity switch 52 takes the form of a commercially availablemagnetically biased reed switch which includes a sensor 54 located onone end of the switch which is operable to close a set of normally opencontacts within the switch when a metal object is moved within apredetermined distance of the sensor. This type of switch is referred toas a proximity switch because it is not necessary that the metallicobject actually contact the sensor in order to trigger the switch. Thesensitivity of the sensor is such that movement of the metallic objectover a distance of approximately 1/10th an and inch toward or away fromthe sensor will shift the switch to an on or an off position.

An elongate switch actuator 56 is mounted between mounting flanges 48 ofthe switch housing for sliding movement longitudinally of the housing. Apair of pins 58 mounted in, and extending between, the flanges 48 retainactuator member 56 within the housing and a leaf spring 63 engagedbetween member 56 and wall 46 of the housing resiliently biases actuatormember 56 firmly against pins 58 to provide a substantial amount offrictional resistance to sliding movement of actuator 56 relative tohousing 40. As best seen in FIG. 3, an actuator tab 62 fixedly securedto or formed on actuator member 56 projects from one side of member 56through a slot 64 in wall 46 into alignment with sensor 54 of switch 52.A pair of projections, defining spaced opposed abutment shoulders 66, 68are fixedly secured to and project from the opposite side of member 56toward the path of movement of piston rod 20. A pin 70 is fixedlysecured to and projects from pivot 32 outwardly from the pivot into thespace between abutment shoulders 66, 68 on actuator member 56.

In FIG. 3, piston rod 20 is shown at its fully retracted end limit ofmovement which corresponds to the unclamped condition of clamp assembly10. With the piston rod 20 at its unclamped end limit of movement, pin70 on pivot 32 is engaged with abutment shoulder 68 and has positionedthe abutment shoulder 68 substantially in engagemeent with the righthand pin 58, which may also function as a stop defining an end limit ofmovement of actuator member 56 to the right relative to housing 40 asviewed in FIG. 3.

With actuating member 56 in the position shown in FIG. 3, its actuatingtab 62 is within actuating proximity of sensor 54 of the proximityswitch, and the switch is in its actuated or switch on position. Theswitch 52 shown in the drawings is provided with a light 72 which willbe illuminated when the switch is on, and a suitable lens 74 in housingcover 42 will make this light visible, thus providing a visibleconfirmation of the location of the clamp assembly in its fully openposition. The electrical contacts of switch 52 will be connected into acontrol circuit to supply this information to the control circuit.

When piston rod 20 is driven from the FIG. 3 position to the left asviewed in FIG. 3 to shift the clamp assembly to its clamped position,pin 70 will be disengaged from abutment shoulder 68 as soon as thismovement starts. However, actuator member 56 will remain in the FIG. 3position and proximity switch 52 will thus remain closed. As piston rod20 approaches its fully extended clamping position, pin 70 will moveinto engagement with abutment shoulder 66 of actuator member 56 andshift the actuator member 56 to the left as viewed in FIG. 3 to moveactuating tab 62 away from the proximity switch sensor 54. The spacingbetween abutment shoulders 66 and 68 is selected to be such that pin 70will not engage shoulder 66 until piston rod 20 is within a relativelyshort distance, say 1/8th of an inch, of its fully extended clampingposition. During this final stage of movement to fully extended endlimit, pin 70 on piston rod 20 will engage abutment shoulder 66 anddrive actuator member 56 to the left a sufficient distance to moveactuating tab 62 out of actuating range of sensor 54. As soon asactuating member 62 moves out of range of sensor 54, the proximityswitch shifts to its switch off position, indicator light 72 will goout, and the control circuit will be signaled by the switch that theclamp is in its clamped position.

Upon subsequent return of piston rod 20 to its unclamped end limit ofmovement, a similar action occurs, that is, switch 52 remains in its offposition until, near the end of its stroke, pin 70 on piston rod 20engages abutment shoulder 68 and returns actuating member 56 to itsswitch on position as the clamp arrives at its fully unclamped position.

While one embodiment of the invention has been described in detail, itwill be apparent to those skilled in the art the disclosed embodimentmay be modified. Therefore, the foregoing description is to beconsidered exemplary, rather than limiting, and the true scope of theinvention is that defined in the following claims.

I claim:
 1. In combination with a power actuated device including arigid member mounted within a fixed frame for movement along a fixedpath relative to said frame between a first end limit of movement and asecond end limit of movement, power actuated means for driving saidrigid member in either direction from one of said end limits to theother, and proximity switch means for signalling the arrival of saidmember at either of said end limits; the improvement wherein saidproximity switch means comprises means defining a slot extending throughsaid frame along said fixed path, a housing fixedly mounted upon saidframe in surrounding relationship to said slot, a proximity switchfixedly mounted in said housing, a proximity switch actuator membermounted in aid housing for sliding movement parallel to said pathbetween a first position wherein said actuator member is withinactuating proximity to said switch and a second position wherein saidactuator meember is out of actuating proximity to said switch, firstabutment means on said rigid member, second abutment means on saidactuator member, one of said abutment means comprising means on one ofsaid members defining an elongate recess terminating at opposite ends inabutment shoulders normal to said fixed path and the other of saidabutment means comprising a projection on the other of said membersprojecting from said other of said members normal to said fixed paththrough said slot in said frame into the recess of said one of saidmembers between said abutment shoulders, said shoulders being spacedfrom each other by a distance such that upon movement of said rigidmember to said first end limit one of said shoulders engages saidprojection and pushes said actuator member into said first position, andupon movement of said rigid member to said second end limit the other ofsaid shoulders engages said projection and pushes said actuator memberinto said second position.
 2. In a power actuated clamp including afixed frame, a fluid pressure actuated motor mounted on said fixed frameand including a piston rod reciprocable along a fixed path relative tosaid frame between a first and a second end limit of movement, clamp armmeans coupled to said piston rod to be located in a clamp closedposition when said piston rod is at one of said end limits and to belocated in a clamp opened position when said piston rod is at the otherof said end limits, and signalling means for signalling the arrival ofsaid clamp arm means at said clamp closed and clamp open positions; theimprovement wherein said signalling means comprises a housing adapted tobe fixedly mounted on said frame, a proximity switch meeans mountedwithin said housing and including on-off switch means and actuatingmeans operable to switch said switch means to its on state upon locationof said actuating means within a first distance from said switch meansand operable to switch said switch means to its off state when saidactuating means is located beyond said first distance from said switchmeans, an actuating member mounted in said housing for movement relativeto said housing along a path parallel to said path of movement of saidpiston rod between a first position and a second position, firstabutment means mounted on said piston rod for reciprocatory movementtherewith, and second abutment means on said actuating member engageablewith said first abutment means as said piston rod approaches one of itsend limits to shift said actuating member from one of said first andsaid second positions to the other as said piston rod arrives at saidone end limit and to move said actuating member from said other positionto said one position as said piston rod arrives at its other end limit.3. The invention defined in claim 2 wherein said second abutment meanscomprises means on said actuating member defining a pair of facingopposed abutment shoulders spaced from each other by a distancesubstantially equal to but slightly less than the length of the strokeof said piston rod between its first and second end limits, and saidfirst abutment means comprises a pin projecting perpendicularly from oneside of said piston rod into the space between said shoulders.
 4. Theinvention defined in claim 2 wherein said actuating member comprises anelongate body mounted for longitudinal sliding movement in said housing,an actuating tab fixedly mounted on and projecting from one side of saidbody in opposed spaced relationship to said switch means to constitutesaid actuating means, and means engaged between said body and saidhousing for frictionally resisting movement of said body relative tosaid housing.